Various types of paving stones or paving elements for use in creating a paved surface are known in the art. In particular, paving stones for creating a paved surface having drainage cavities or holes formed therein are known. Generally, such drainage cavities are provided to prevent liquids (e.g. water) from pooling on the paved surface by allowing passage of such liquids there-through.
Some attempts have also been made at providing filtering of liquids being drained through the drainage cavities. Filtering is provided, for example, by providing a filter media within the drainage cavities such that the liquid being drained through the drainage cavity is filtered by the filter media. In this way, various contaminants which may be present in the drainage liquid, such as oil, particulates and other chemicals, are retained by the filter media. Filtration of the drainage liquid is generally desirable for the purposes of reducing the amount of contaminants reaching the groundwater and soil beneath the paved surface, as well as any receiving waters that the drainage liquid may be discharged into.
For example, U.S. Pat. No. 5,342,142 to Barth et al. describes an angular paving stone having a number of recesses. The recesses are configured such that when the paving stones are laid, full recesses are formed by the recesses of the adjacent stones complementing each other. The full recesses allow water to be discharged from a paved surface into the layer underneath. Barth describes that the full recesses may be filled with a suitable filling material such as sand, fine gravel, fine chips or the like, and that any “filling material plugs” which may form over time can be swept away using, for example, a motor sweeper. However, the full recesses formed by laying the paving stones are not described as being configured to facilitate cleaning of the recesses by means other than by sweeping. Furthermore, it has been found that the filling material generally cannot be easily removed from the recesses, since attempting to remove such material can result in the filling material being pushed deeper into the recesses in some cases, as further described below.
In another example, U.S. Pat. No. 4,834,575 to Barth et al. describes a paving stone for forming a paved surface by laying similarly configured paving stones adjacent to one another, in which there is a free space created between adjacent paving stones for discharging water. In one aspect, the paving stone is described as including a protrusion having a chamfered upper face that slopes downwardly, such that when neighbouring paving stones are laid adjacent to each another, the corresponding protrusions of the stones face each other to create the free space there-between. While it is described that the free space may be filled with water permeable filling material such as fine grained gravel, the paving stones are not specifically configured to allow such filling material to be readily removed once the filling material becomes contaminated or otherwise accumulates pollutants.
U.S. Pat. No. 4,997,308 to Welling, Jr. describes a paving stone having four angled corners and a central hole. The edges of the upper surface of the paving stone are described as being chamfered. The central hole is described as being provided for the purpose of facilitating handling of the paving stones among other purposes. However, the central hole is not described as being configured to be filled with any material which acts as a filter media.
For pavement systems that incorporate drainage cavities and/or filter media, a problem has been the challenge of maintaining the infiltration capacity, i.e. the volume of water able to be captured and treated by the system. Whether planning, designing, constructing and/or managing a permeable pavement installation, it is fundamentally important to provide and maintain surface infiltration capacity. However, studies have consistently shown reductions in infiltration capacities as such pavement systems age, due to clogging of the filter media with organic and chemical particulates such as heavy metals, nutrients, sediment and organic matter. Furthermore, studies have shown that employing conventional street cleaners with such systems resulted in limited restoration in infiltration capacity. If the infiltration capacity of a pavement system cannot be substantially restored by cleaning methods, it is inevitable that the infiltration capacity will decrease with age until the system is no longer able to capture and treat water effectively.
Accordingly, there remains a need for a paving element and a system that addresses at least one of the deficiencies known in the art.